FIG. 1 shows a configuration disclosed in Patent Literature 1 as a conventional example of the optical-connector-incorporating plug of this type, and FIG. 1 also shows a mating adapter to which the optical-connector-incorporating plug (referred to as a housing in Patent Literature 1) is connected.
An optical-connector-incorporating plug 10 includes a tube portion 11, an outer tube portion 12, a coupling body 13, and a cable 14. The tube portion 11 has a joining portion 11a at a front end thereof, and in the joining portion 11a, a supporting portion 11b for supporting an optical connector 15 such that it can move in the axial direction of the tube portion is disposed. In the supporting portion 11b, a through-hole 11c is formed, and a mounting member 16 mounted to the optical connector 15 is inserted into the through-hole 11c. 
The tube portion 11 has a partition wall 17 fixed at a position closer to a base end of the tube portion 11 than the supporting portion 11b, and the partition wall 17 has a through-hole 17a that lets an optical fiber 14a exit therethrough. A coil-shaped spring 18 is disposed between the partition wall 17 and a flange portion 16a of the mounting member 16, and the mounting member 16 and the optical connector 15 are biased toward a front end of the tube portion 11 in the axial direction by the force exerted by the spring 18.
An adapter 20 is fixed to a body 21 so as to cover an optical module 22 partially sticking out of the body 21. The adapter 20 has a joining portion 20a that is jointed to the tube portion 11 of the optical-connector-incorporating plug 10. The front end of the optical module 22 sticks out of a through-hole 20b formed in the adapter 20.
The optical module 22 has an insertion hole 22a into which the optical connector 15 of the optical-connector-incorporating plug 10 is inserted, and a ferrule 22b, which is connected to a ferrule 15a of the optical connector 15, is provided in the insertion hole 22a. 
The optical-connector-incorporating plug 10 is joined and connected to the adapter 20 while the joining portion 20a of the adapter 20 is inserted between the outer tube portion 12 and the tube portion 11 of the optical-connector-incorporating plug 10. The optical connector 15 moves toward the base end in the axial direction, against the force exerted by the spring 18, and because of this force (resilience) exerted by the spring 18, the optical connector 15 is pressed toward the optical module 22, and consequently a good connection state can be ensured between the ferrules 15a and 22b. 